The present invention relates in general to motor vehicle suspension systems which include variable damping shock absorbers and controllable springs, for example air springs, and, more particularly, to a speed dependent method for controlling;the shock absorbers and springs.
Motor vehicle suspension systems are connected between the body of the vehicle and the wheels to determine the ride and handling of the vehicle. Conventional suspension systems include springs and shock absorbers which are fixed such that the ride and handling are fixed as well.
More advanced suspension systems include controllable elements such as variable damping shock absorbers which permit two or more damping factors to be selected as needed. Controllable springs may also be included. Such springs are typically pneumatically or air controlled and are inflated to increase the spring rate of the overall vehicle spring system and deflated to decrease the spring rate.
In prior art suspension systems, the shocks and springs may be manually controlled by the operator of the vehicle. Automatic control is also utilized to control the shocks and springs in response to inputs from the vehicle as well. For example, the lateral acceleration of the vehicle may be determined and compared to a threshold to determine whether to make adjustments to the vehicle suspension. Unfortunately, known prior art systems do not utilize the relation of the speed of the vehicle to lateral acceleration in making suspension adjustment decisions. Accordingly, there is a need for an improved suspension control system which includes vehicle speed in making suspension control decisions based on lateral acceleration to eliminate the compromises which are made in the prior art between low speed performance and high speed performance.